Infectious spondylitis secondary to a mycotic aortic aneurysm

A 58-year-old man presented with lombalgia and shriving for 6 days. He had a history of HIV infection under treatment. Blood analysis showed leukocytosis (18.430/L), urine analysis was unremarkable and haemocultures revealed the presence of Klebsiella Pneumoniae. The patient was started on amoxicillin + clavulanic acid 875 mg + 125 mg. It was performed a spinal MRI and an urgent CT angiography. The patient was admitted to the infectious diseases department. Following the forward imaging findings, particularly the aneurysm diameter increasing (51mm to 55mm in 26 days), the patient underwent open vascular surgery to remove the infected thrombosed aneurysm. Candida albicans was isolated from the excluded aneurysm and the patient was prescribed Caspofungin 70mg.

Fig 1. Sagittal T1-WI (1a), T1-WI post gadolinium (1b), and T2-WI STIR (1c) show bone marrow oedema of L2 and L3 vertebras (*) without features of disc involvement. Additionally, there is an anterior paravertebral and a ventral epidural collection that enhances after contrast administration (arrows). Sagittal angio-CT (1d) shows a thrombosed abdominal aorta aneurysm (arrows) adjacent to the L2-L3 vertebras.

Fig 2. Axial T2-WI (2a) and T1-WI post gadolinium (2b) show a mural thrombus in the abdominal aorta (arrow) with a post-contrast enhancement of the ventral epidural collection and peri-vertebral collection. Angio-CT (2c) shows a 51mm thrombosed abdominal aorta aneurysm (*).

Fig 3. Axial (3a) and Sagittal (3b) angio-CT images were performed around 50 days after the Fig 1. and Fig 2. exams, and 9 days after vascular surgery. There is a relevant progression of L2-L3 endplate destruction (*), and a persistency of pre-vertebral collection, predominantly hypodense with a mild enhancement ring.

Background

Infected aortic aneurysms are uncommon. Risk factors include diabetes mellitus, renal disease and immunosuppression. Staphylococcus and Salmonella are the most identified pathogens, with fungal infections being a minority (Candida albicans and Aspergillus). Synchronous or metachronous infected aneurysms can occur in up to one-third of the cases [1]. Infected aortic aneurysms and Spondylitis co-occurrence have been reported. Proposed mechanisms of vertebral involvement secondary to an aortic aneurysm include pseudoaneurysm formation due to contained ruptures, arterial pulsation with chronic osseous ischemia, a direct extension of infection or haematogenic spread [2,3].

Clinical Perspective

Clinical symptoms may include back pain, fever, and gastrointestinal abnormalities. The physical examination can show a pulsatile mass, stiffness of the spine and localized vertebral tenderness at palpation of the back. As these symptoms are unspecific, imaging modalities like CT and MRI are fundamental to the diagnosis.

Imaging Perspective

Contrast-enhanced CT scan of the abdomen and spine can show 1) a focal dilatation of the abdominal aorta (measuring 50% greater than the proximal normal segment, or >30mm of maximum diameter), with or without intramural irregular hypodense thrombus; 2) paravertebral soft tissue anomalies as periaortic fluid, gas, hematomas or collections (e.g., psoas abscess); 3) vertebral bone erosion with/without a contiguous extending mass. Although the extent of related bony destruction is better defined on CT images than on MRI, the late is relevant to assess osteomyelitis and adjacent paravertebral collections. MRI protocol should include T1, STIR or fat-suppressed T2 and fat-suppressed postcontrast T1.

Outcome

Imaging should be performed to discard other infected aneurysms, identify complications, map relevant vascular anatomy for treatment planning and monitor treatment efficacy. Therapeutic options include open surgery, endovascular stenting, endovascular embolization, medical therapy, or a combination of these. Antibiotic therapy should be implemented according to isolated pathogens from haemocultures, abscesses or biopsy material. In this case, Candida albicans was isolated from the surgically excluded aneurysm. The prognosis of a mycotic aortic aneurysm is very poor [2,4]. Moreover, as Klebsiella Pneumoniae was found in the haemocultures, it was assumed that it was a superinfection leading to a spondylitis. The patient accomplished 42 days of anti-fungal (first caspofungin 70mg and then fluconazole 400mg) and 85 days of antibiotic therapy (amoxicillin + clavulanic acid 875 mg + 125 mg).

Take Home Message / Teaching Points

The primary site of infection in patients with concurrent spondylitis and mycotic aneurysm may be either the aorta or the spine (Spontaneous infective spondylitis).

Contrast-enhanced CT scan is very useful to detect aortic aneurysms and study vertebral bone erosions. MRI protocol should include T1, STIR or fat-suppressed T2 and fat-suppressed postcontrast T1.

Written informed patient consent for publication has been obtained.